What might it mean to say that language is innate or, alternatively, that language must be learned? This proposal attempts to articulate these questions in terms that lend themselves to experimental investigation, asking which aspects of language development are so overdetermined in humans that they will appear even under learning conditions that vary widely from the typical. The subjects of the studies are deaf children whose hearing parents have not yet exposed them to sign language, and whose hearing losses are so profound as to preclude the acquisition of spoken language. Despite their lack of an accessible conventional language to use as a model for communication, these children do communicate and do so using a gestural system that is structured at both word and sentence levels. Moreover, the gestures they use are structured differently from the gestures used by the hearing individuals around them. Although the deaf children's gesture systems are not patterned after the spontaneous gestures of their hearing parents, it is possible that other non-linguistic aspects of the children's social environment influence the structure of their gestures. In order to determine the extent to which the structures in the deaf children's gestures are shaped by the way in which mothers and children jointly interact in their culture -- and in so doing, explore the "resilience" of these structures across wide cultural variation -- deaf children of hearing parents in a second culture will be observed. Study 1 explores the interactions of hearing mothers and their deaf children (ages 3-5) in Taiwan and in America, testing the hypothesis that mothers interact differently with their children in Chinese and American cultures. Study 2 explores the spontaneous gestures produced by Chinese and American mothers when interacting with their deaf children, clarifying the gestural model presented to the deaf child in each culture. If the mothers in the two cultures do provide their deaf children with different gestural models, do the deaf children's gesture systems more closely resemble their mothers' gesture systems or one another's? Study 3 analyzes the gestures produced by the Chinese deaf children, and compares them to the gestures produced by the American deaf children. It is precisely the properties of language which are found in the gestures of both groups of children (and not in the gestures of the mothers) that can be said to be resilient across cultural variation. Study 4 attempts to put these studies of gesture in a cultural context by exploring the gestures of hearing mothers and their hearing children (ages 3-5) in each culture, and comparing these observations to the data gathered on the Chinese and American hearing mothers and their deaf children.